1. Field of the Invention
The present invention relates to an image signal processing apparatus for selectively reproducing and processing plural kinds of image signals transmitted in different television systems, and more particularly to an image signal processing apparatus wherein a sync signal component is obtained from each input image signal by sync reproducing means using a DSP (Digital Signal Processor).
2. Description of the Related Art
As is well known, the broadcasting media have recently been diversified in accordance with developments in digital technology. In particular, in addition to TV broadcasting of NTSC system using VHF band and UHF bands of ground waves, there have been realized, for example, TV broadcasting of NTSC system using a BS (Broadcasting Satellite) and TV broadcasting of high image quality (high vision) of MUSE system.
FIG. 1 shows a conventional TV receiver developed to meet requirements of diversified broadcasting media. The TV receiver has a function of selectively reproducing signals of NTSC TV broadcasting and MUSE TV broadcasting. In FIG. 1, numeral 11 denotes an input terminal. The input terminal 11 is supplied selectively with image signals of analog base bands transmitted in the NTSC or MUSE systems.
The image signal supplied to the input terminal 11 is delivered to a clamp circuit 12, and the level of the image signal is adjusted. Then, the output from the clamp circuit 12 is fed to an A/D (analog/digital) conversion circuit 13 and converted to digital image data. The digital image data output from the A/D conversion circuit 13 is supplied to an NTSC sync reproducing circuit 14, an NTSC decoder 15, a MUSE sync reproducing circuit 16 and a MUSE decoder 17.
When the image signal supplied to the input terminal 11 is an NTSC image signal, the NTSC sync reproducing circuit 14 is driven. On the basis of the input digital image data, the NTSC sync reproducing circuit 14 generates a clock, a horizontal sync signal, etc. corresponding to the NTSC system and outputs them to the NTSC decoder 15. The NTSC decoder 15 subjects the input digital image data to decoding processing on the basis of the clock, horizontal sync signal, etc. generated by the NTSC sync reproducing circuit 14. Thus, the NTSC image signal is reproduced.
When the image signal supplied to the input terminal 11 is a MUSE image signal, the MUSE sync reproducing circuit 16 is driven. On the basis of the input digital image data, the MUSE sync reproducing circuit 16 generates a clock, a horizontal sync signal, etc. corresponding to the MUSE system and outputs them to the MUSE decoder 17. The MUSE decoder 17 subjects the input digital image data to decoding processing on the basis of the clock, horizontal sync signal, etc. generated by the MUSE sync reproducing circuit 16. Thus, the MUSE image signal is reproduced.
The digital image data output from the NTSC decoder 15 or MUSE decoder 17 is selected by a switch 18 and taken out from an output terminal 19. When the image signal supplied to the input terminal 11 is an NTSC image signal, the switch 18 is operated to pass the output of the NTSC decoder 15 to the output terminal 19. On the other hand, when the image signal supplied to the input terminal 11 is a MUSE image signal, the switch 18 is operated to pass the output of the MUSE decoder 17 to the output terminal 19. Thereby, NTSC TV broadcasting or MUSE TV broadcasting are selectively reproduced.
The NTSC sync reproducing circuit 14 outputs a control signal for controlling the level adjustment in the clamp circuit 12 for an NTSC image signal, and the MUSE sync reproducing circuit 16 outputs a control signal for controlling the level adjustment in the clamp circuit 12 for a MUSE image signal. The control signal from the circuit 14 or 16 is selected by a switch 20 and supplied to the clamp circuit 12.
When the image signal supplied to the input terminal 11 is the NTSC image signal, an switch 20 is operated to pass the control signal from the NTSC sync reproducing circuit 14 to the clamp circuit 12. On the other hand, when a image signal supplied to the input terminal 11 is the MUSE image signal, the switch 20 is operated to pass the control signal from the MUSE sync reproducing circuit 16 to the clamp circuit 12.
In the above conventional TV receiver, the NTSC sync reproducing circuit 14 and NTSC decoder 15 are provided to reproduce an NTSC image signal, and the MUSE sync reproducing circuit 16 and MUSE decoder 17 are provided to reproduce a MUSE image signal. In other words, reproducing circuits are provided individually for reproducing signals transmitted by different broadcasting media. As a result, the size and cost of the apparatus increase considerably, and the practicability of the apparatus is low.